Many cardiac arrhythmias can be treated by selectively blocking pathways or sources of electrical activation in the myocardial tissue by catheter ablation. The application of an ablation medium (such as radio-frequency current, extreme cold, ultra-sound, laser, etc.) triggers cell death of electrically conducting myocytes and the formation of a non-conducting lesion.
Cryosurgery is the application of extreme cold to ablate abnormal or diseased tissue. Cryosurgery works by taking advantage of the destructive force of freezing temperatures on cells. At low temperatures, ice crystals may form inside the cells, which can tear them apart. More damage may occur when blood vessels supplying the tissue freeze.
In the case of a catheter leak, there is the danger that refrigerant or another ablation medium can enter the patient's body. There is also the danger that blood or any other physiological material enters and damages the ablation system in the case of a catheter leak.
Methods for exhausting a refrigerant from a cryoablation system by a vacuum are described in U.S. Pat. No. 3,859,986 or WO 99/65410.
In cryoablation systems, extreme cold (particularly temperatures below −50° C.) are generated in the boiling chamber of a cryo-applicator (the therapeutic component in wall contact with the tissue) by vaporizing a refrigerant (Joule-Thompson effect). The pathway of refrigerant flow (supply line, throttle, boiling chamber, return or drain line) is sealed by a continuous outer jacket. When connecting a vacuum source to the return line, the refrigerant is exhausted actively from the low pressure stream of the catheter. This involves technical challenges.
In the case of leakage, blood might be sucked into the catheter. For avoiding an unacceptable loss of blood (hemorrhagic shock) proper technical measures are needed which should attenuate the consequences of a loss of blood. For this purpose, blood detection systems are described in EP 1,148,833. Due to the high risk level also two or more redundant or complementary blood detectors are used.
Methods for controlling a pressure within an ablation device are described in U.S. Pat. No. 7,004,936. Cryogenic catheters might be operated at two different flow conditions (normal flow for ablation and low flow for cryomapping). Here the use of a vacuum drain might decrease the boiling chamber pressure below the static triple point pressure of the cooling medium. Methods for maintaining a sufficiently high boiling point pressure at a low flow rate are described in U.S. Pat. No. 6,589,234.
However, conventional ablation systems may still suffer from the shortcoming that in case of a leak in an ablation catheter, it is difficult to reliably suppress blood flow into the catheter.